The present invention relates generally to methods and apparatus for use in disk drives for computer systems, and more particularly, to methods and apparatus for preventing damage to disk drive heads by latching an actuator assembly of a disk drive.
Disk drives typically include mechanisms which are arranged to "park" disk drive heads when the disks in the disk drive of a computer system are not in use. Parking a disk drive head entails positioning the disk drive head over a particular section of a disk, and latching an actuator which supports the disk drive head in order to lock the disk drive head in place. As any sudden, abrupt contact between a disk drive head and a disk may result in damage to the disk and, hence, the potential loss of data in the event that the disk drive head abruptly contacts a data-carrying sector of the disk, parking the disk drive head serves to protect the data sectors of the disk. It should be appreciated that the ability to park disk drive heads to prevent sudden contact between the disk drive heads and data sectors of the disk is crucial.
A disk drive head is typically coupled to an actuator assembly. An actuator assembly is arranged to pivot or linearly move the disk drive head to different positions over a disk such that data may be retrieved from different data-carrying sectors of the disk. In general, when a disk drive head is to be moved, force is generated to pivot or move the actuator assembly through the use of a coil structure that is a part of the actuator assembly, and a magnetic field which surrounds the coil structure, as will be appreciated by those skilled in the art. By passing current through the coil structure in a particular direction and for a specified length of time, the actuator assembly may be pivoted such that the disk drive head is positioned over a specific portion of the disk.
The forces associated with parking a disk drive head are often quite substantial. That is, the force that is generated by pivoting or linearly moving the actuator assembly in order to place the disk drive head in a parked position is generally relatively high. A disk drive head parking process during which the actuator assembly is moved with a relatively high force may be considered to be a "hard stop." During a hard stop, shocks to the actuator assembly may cause damage to the disk drive heads. As such, mechanisms are often implemented in disk drives to prevent damage to disk drive heads during parking processes.
One mechanism that is conventionally used to park disk drive heads is a mechanical latch assembly which captures a portion of the actuator assembly. Such a mechanical latch assembly usually involves mechanically capturing the actuator assembly to park the disk drive heads. Although mechanical latch assemblies are effective in holding disk drive heads in a fixed position, the processes of parking and "un-parking" disk drive heads are inefficient, as positioning and repositioning mechanical pieces is relatively time-consuming. In addition, tolerancing a plurality of mechanical parts such that a mechanical latch assembly may function as desired is both difficult and time-consuming.
Another latching mechanism that is often used to park disk drive heads involves solenoids that are arranged to lock an actuator assembly and, therefore, disk drive heads into place. As tolerances associated with placing solenoids with respect to an actuator assembly are relatively easy to meet, solenoids are effective for use in latching actuator assemblies. In addition, the amount of time associated with activating a solenoid to latch an actuator assembly is minimal. However, although solenoids are effective and efficient when used as latching mechanisms, the physical size of solenoids is typically inhibitive. That is, solenoids, as well as associated circuitry which is used to activate and to deactivate the solenoids, consume substantial amounts of space within a disk drive and, as a result, are not always desirable. Further, solenoids are typically expensive, and are, therefore, often impractical for use in high-volume products like disk drives.
Magnetic latches have also been used to lock actuator assemblies. When a magnetic latch is used to lock an actuator assembly, a coil assembly in the actuator assembly is used, in conjunction with a magnetic field generated around the coil assembly, to force a ferrite component, or piece, on the actuator assembly towards a stationary locking magnet. Once the ferrite piece on the actuator assembly is forced towards the locking magnet, magnetic attraction between the ferrite piece on the actuator assembly and the locking magnet causes the two parts to come together, thereby locking the actuator assembly in a stationary position, as will be described with respect to FIG. 1a.
FIG. 1a is a diagrammatic representation of a cross-section of a conventional stationary magnetic latching structure. A stationary magnetic latching structure 110 includes a stationary magnet 112, a rubber pad 114, and an extension of a magnetic steel plate 116. The extension of magnetic plate 116 shunts fringe fields from stationary magnet 112, as will be appreciated by those skilled in the art. The extension of magnetic plate 116 also essentially serves to secure stationary magnet 112, as well as rubber pad 114, with respect to extension of magnetic plate 116.
Rubber pad 114, which is also known as a crash stop, serves to absorb some of the force produced by the contact of an actuator assembly 120 with stationary magnet latching structure 110. When current flows through a coil assembly (not shown) that is associated with actuator assembly 120, an actuator ferrite piece 122 that is attached to actuator assembly 120 is moved towards stationary magnet 112. Once actuator ferrite piece 122 begins to move towards stationary magnet 112, attractive forces between stationary magnet 112 and actuator ferrite piece 122 further propel actuator ferrite piece 122 towards stationary magnet 112.
If actuator ferrite piece 122 and stationary magnet 112 are allowed to latch directly together during a parking process, damage may occur to the disk drive heads, due to the fact that such a direct "collision" between actuator ferrite piece 122 and stationary magnet 112 is, in essence, a physical shock to the disk drive heads. As such, rubber pad 114 is included in stationary magnet latching structure 110 to absorb some of the force associated with the attraction between stationary magnet 112 and actuator ferrite piece 122. Rubber pad 114 briefly compresses when actuator ferrite piece 122 makes contact with rubber pad 114, and expands once actuator ferrite piece 122 settles into a parked position, e.g., an equilibrium position with respect to stationary magnet 112.
In general, the pliant properties of rubber makes the size of rubber pad 114, difficult to control, as forming a rectangular piece of rubber is difficult in light of the properties of rubber. If the size of rubber pad 114 is not properly proportioned, that is, if the size of rubber pad 114 is not appropriate for the force at which actuator ferrite piece 122 is attracted towards stationary magnet 112, damage may occur to disk drive heads either because actuator ferrite piece 122 is improperly latched to stationary magnet 112, or because not enough force is absorbed by rubber pad 114. Further, as rubber pad 114 is typically rectangular in shape, the precise placement of rubber pad 114 in a desired location within an overall disk drive assembly is difficult, as will be appreciated by those skilled in the art. As such, the proper formation and the precise placement of magnetic latching assembly 110 often proves to be unduly time-consuming.
The inclusion of rubber pad 114 on stationary magnet 112 creates an air gap between actuator ferrite piece 122 and stationary magnet 112. It should be appreciated that the air gap is essentially defined by the thickness of rubber pad 114. Such an air gap requires that the magnetic attraction between stationary magnet 112 and actuator ferrite piece 122 be strong enough to permeate the air gap and still hold stationary magnet 112 and actuator ferrite piece 122 together when desired. In general, the impact force between actuator assembly 120 and stationary magnet latching structure 110 increases as the size, i.e., the inertia, of actuator assembly 120 in the overall disk drive increases. As such, the size of rubber pad 114 generally also increases to compensate for the additional impact force which must be absorbed to prevent damage to disk drive heads (not shown).
When the size of rubber pad 114 increases, it follows that the strength of stationary magnet 112 and the size of actuator ferrite piece 122 are typically also increased in order to enable the magnetic attraction between stationary magnet 112 and actuator ferrite piece 122 to pass through the air gap. As a result, the possibility of magnetic fields associated with stationary magnet 112 interfering with other portions of the overall disk drive increases. In general, it should be appreciated that the air gap between stationary magnet 112 and actuator ferrite piece 122 results in the inefficient use of magnetic fields associated with stationary magnet 112. In other words, the magnetic holding force between stationary magnet 112 and actuator ferrite piece 122 is less efficiently used as the size of the air gap increases.
Therefore, what is desired is a method and an apparatus for efficiently and effectively positioning disk drive heads in a parked position within a disk drive assembly without damaging the disk drive heads. Further, what is desired is an efficient method and an apparatus for parking disk drive heads which is inexpensive and relatively easy to implement.